Consequences of revised CLSI and EUCAST guidelines for antibiotic susceptibility patterns of ESBL- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates.

OBJECTIVES: This study aimed to: (i) analyse the antibiotic susceptibility testing (AST) profiles of extended spectrum β-lactamase (ESBL)- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates applying EUCAST 2013 AST guidelines; and (ii) evaluate discrepancies in AST profiles according to EUCAST 2010 guidelines, EUCAST 2013 guidelines, CLSI 2009 guidelines and CLSI 2013 guidelines.
METHODS: The 195 ESBL- and/or AmpC β-lactamase-producing Enterobacteriaceae isolates used in this study were systematically characterized by disc diffusion AST interpreted according to the 2013 guidelines of EUCAST and CLSI, the EUCAST 2010 guidelines and the CLSI 2009 guidelines.
RESULTS: Individual cephalosporin AST patterns according to EUCAST 2013 guidelines were described for individual ESBL and AmpC β-lactamase genotypes. Significant differences in the susceptibility rates of important cephalosporins such as cefepime, ceftazidime and cefotaxime applying EUCAST 2013 and CLSI 2013 AST guidelines were demonstrated for ESBL- and AmpC β-lactamase-producing isolates.
CONCLUSIONS: The confirmation of ESBL and/or AmpC β-lactamase production can support the selection of an adequate antibiotic drug therapy. Despite a harmonized CLSI and EUCAST 'report as found' strategy for cephalosporins and ESBL-producing isolates, AST interpretation according to the CLSI 2013 and EUCAST 2013 guidelines shows significant differences in susceptibility rates for mainstay cephalosporins such as cefepime, ceftazidime and cefotaxime. Thus, further harmonization of clinical breakpoints is warranted.